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Applies to clemastine: compounding powder, oral syrup, oral tablet

Nervous system

Nervous system side effects have included central nervous system depression which has commonly resulted in drowsiness, dizziness, and headache. Dyskinesias have rarely been reported following chronic use of antihistamines.[Ref]

Nearly all patients experience drowsiness. This drowsiness may subside in some patients with extended use. Patients should be warned against driving, as well as concomitant ingestion with alcohol and other sedative-hypnotic drugs.

Few cases of dyskinesias and tremors, often of the face, have been reported in patients whose chronic use of antihistamines extended over a period of 3 to 10 years. Some of these cases were only partially relieved by discontinuation of the drug. Haloperidol was successful in relieving symptoms.[Ref]

Gastrointestinal

Gastrointestinal side effects have included dry mouth and constipation due to anticholinergic effects. This has occurred in up to one-third of patients.[Ref]

Cardiovascular

Cardiovascular side effects have included hypotension, tachycardia, and palpitations.[Ref]

Ocular

Ocular effects are due to the anticholinergic effects and may include blurred vision, diplopia, and dry eyes.[Ref]

Genitourinary

Genitourinary side effects have included dysuria, urinary hesitancy, decrease in urine flow, and in rare cases, acute urinary retention.[Ref]

Hematologic

Hematologic side effects that have been reported with antihistamines include bone marrow suppression, thrombocytopenia, and aplastic anemia.[Ref]

A fatal case of agranulocytosis has been reported in a patient taking chlorpheniramine, pseudoephedrine, acetaminophen, dextromethorphan, phenylpropanolamine, and aspirin. Chlorpheniramine was felt to be the cause.[Ref]

Respiratory

Respiratory side effects have included thickening of bronchial secretions, wheezing, and tightness in the chest.[Ref]

Dermatologic

At least one case of toxic pustuloderma has been reported during clemastine therapy.[Ref]

Professional resources

Related treatment guides

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